1. Field of the Invention
The present invention relates to a plasma processing apparatus used for processing semiconductor wafers and the like by the action of a plasma generated by microwave.
2. Description of the Background Art
In recent years, semiconductor products have been increased in density and reduced in size to a great degree. Accordingly, some manufacturing processes of the semiconductor products employ a plasma processing apparatus for such processing as film deposition, etching and ashing. In particular, there is a tendency to use a microwave plasma apparatus since the microwave plasma apparatus can produce a plasma in a stable manner even in a high-vacuum state of a relatively low pressure, specifically from about 0.1 to several tens of mTorr, by using the microwave or a combination of the microwave and a magnetic field from a ring-shaped coil to produce a high-density plasma.
Such a microwave plasma processing apparatus is disclosed for example in Japanese Patent Laying-Open Nos. 3-191073 and 5-343334 and Japanese Patent Laying-Open No. 9-181052 filed by the applicant of the present application. A general plasma processing apparatus using the microwave is described briefly below in conjunction with FIGS. 11 and 12. FIG. 11 shows a structure of a conventional and generally employed plasma processing apparatus and FIG. 12 is a plan view of a planar antenna member.
Referring to FIG. 11, a plasma processing apparatus 2 includes a process chamber 4 which can be evacuated, a mount base 6 on which a semiconductor wafer W is mounted, and an insulating plate 8 provided in an airtight manner on a ceiling opposite to mount base 6. Insulating plate 8 transmitting microwave is formed of aluminum nitride or the like in the shape of a disk, for example.
Plasma processing apparatus 2 further includes, on the upper side of insulating plate 8, a planar antenna member 10 in the shape of a disk with a thickness of several millimeters as shown in FIG. 12 and a wave-delay member 12 formed of a dielectric for example for decreasing the wavelength of microwave in the radial direction of planar antenna member 10 as required. In addition, plasma processing apparatus 2 includes a ceiling cooling jacket 16 above wave-delay member 12 that has a cooling channel 14 formed for flowing a cooling water therein in order to cool wave-delay member 12 and the like. Antenna member 10 includes a great number of microwave radiation holes 18 that are through holes nearly circular or in the shape of slit (circular holes are shown in FIG. 12). In general, microwave radiation holes 18 are arranged concentrically as shown in FIG. 12 or spirally. An internal cable 22 of a coaxial waveguide 20 is connected to the central part of planar antenna member 10 for guiding a microwave of 2.45 GHz for example produced by a microwave generator (not shown). The microwave is transmitted radially in the radial direction of antenna member 10 and also discharged from microwave radiation holes 18 provided in antenna member 10 to be transmitted downward through insulating plate 8 into process chamber 4. The microwave causes a plasma in process chamber 4 for performing a predetermined plasma process such as etching and film deposition for a semiconductor wafer.
When the plasma processing apparatus as described above is used to carry out a predetermined plasma process for semiconductor wafer W, the plasma process must be performed uniformly over the wafer surface in order to enhance the yield. Then, it is required to render the plasma density uniform in a process space S directly above the wafer surface.
However, the plasma density tends to be considerably higher in the central portion of process space S, which is directly below the central part of planar antenna member 10 as described above that has no microwave radiation hole 18 provided therein, namely so-called blind part 24, compared with the density of the peripheral portion surrounding the central portion of process space S. A resultant problem is that the plasma density has a lower uniformity. FIG. 13 shows a graph illustrating a plasma density distribution in the process space where the supplying power of the microwave is varied successively from 700 to 2000 W (watt). According to this graph, the plasma density of the wafer central part (central portion of process space S) is remarkably higher than that of the peripheral part and thus the plasma density is undesirably nonuniform. This problem arises possibly for the reason described below. When the apparatus operates, planar antenna member 10 acts as an upper electrode while mount base 6 acts as a lower electrode so that a capacitive coupling component is generated between these electrodes, which results in a so-called parallel-plate mode of the microwave. Thus the microwave transmitted from the central part of planar antenna member 10 to the peripheral part is reflected from the peripheral part and accordingly returned to and concentrated in the central part. Then, although no microwave radiation hole 18 is provided in the central part, the microwave is radiated downward from blind part 24 at the central part.
One object of the present invention is to provide a plasma processing apparatus with an improved planar uniformity of the plasma density in a process space.
A plasma processing apparatus according to one aspect of the present invention includes a process chamber including an opened ceiling and an internal space which can be evacuated, an insulating plate airtightly attached to the ceiling of the process chamber, a mount base placed in the process chamber for mounting thereon a workpiece to be processed, a planar antenna member placed above the insulating plate and including a microwave radiation hole for transmitting therethrough microwave used for generating plasma, the microwave transmitted through the insulating plate into the process chamber, gas supply means for supplying a predetermined gas into the process chamber, and a shield electrode member placed between the insulating plate and the planar antenna member for partially blocking out radiation of the microwave from the planar antenna member.
In the structure described above, a part of radiation of the microwave from the planar antenna member is blocked out and thus the part of radiation is not supplied into the process space. Then, an appropriate selection of any portion blocking out the microwave makes it possible to enhance the planar uniformity of the plasma density.
Typically, the shield electrode member blocks out radiation of microwave from the center and a part therearound of the planar antenna member. In this way, the plasma density in the central portion of the process space can be lowered to further enhance the planar uniformity of the plasma density.
In order to block out radiation from the center and the part therearound of the planar antenna member, the shield electrode member includes, for example, a disk-shaped electrode body placed opposite the center and the part therearound of the planar antenna member, a ring-shaped conductive frame placed to concentrically surround the electrode body, and a conductive arm connecting the electrode body and ring-shaped conductive frame and supporting the electrode body.
Preferably, the conductive arm is displaced from the microwave radiation hole of the planar antenna member. Then, the microwave radiated from the microwave radiation hole is not absorbed by the conductive arm and is accordingly supplied into the process chamber, so that the efficiency of use of the microwave can be enhanced.
According to one preferred embodiment, the shield electrode member includes a microwave transmission window corresponding in position to the microwave radiation hole of the planar antenna member. When the planar antenna member includes a plurality of microwave radiation holes formed at a predetermined pitch, the shield electrode member includes microwave transmission windows respectively corresponding in position to the microwave radiation holes. Thus, the microwave radiated from the microwave radiation holes is not absorbed by the conductive arm and is accordingly supplied into the process chamber, so that the efficiency of use of the microwave can be enhanced.
The microwave transmission windows include for example a through hole pierced through the shield electrode member and a through recess cut inward from the periphery of the shield electrode member.
The shield electrode member is placed apart from the planar antenna member, for example. In this case, a protection plate may be placed between the shield electrode member and the planar antenna member for preventing discharge from occurring between the shield electrode member and planar antenna member. In this way, abnormal discharge can be prevented from occurring between the shield electrode member and planar antenna member. Here, as another example, the shield electrode member may be bonded to be secured onto the insulating plate by an adhesive.
A plasma processing apparatus according to another aspect of the present invention includes a process chamber including an opened ceiling and an internal space which can be evacuated, an insulating plate airtightly attached to the ceiling of the process chamber, a mount base placed in the process chamber for mounting thereon a workpiece to be processed, a planar antenna member placed above the insulating plate and including a plurality of microwave radiation holes formed at a predetermined pitch for transmitting therethrough microwave used for generating plasma, the microwave transmitted through the insulating plate into the process chamber, gas supply means for supplying a predetermined gas into the process chamber, and a shield electrode member placed between the insulating plate and the planar antenna member for blocking out radiation of the microwave from the center and a part therearound of the planar antenna member.
According to still another aspect of the present invention, a plasma processing apparatus includes a process chamber including an opened ceiling and an internal space which can be evacuated, an insulating plate airtightly attached to the ceiling of the process chamber, a mount base placed in the process chamber for mounting thereon a workpiece to be processed, a planar antenna member placed above the insulating plate and including a plurality of microwave radiation holes formed at a predetermined pitch for transmitting therethrough microwave used for generating plasma, the microwave transmitted through the insulating plate into the process chamber, gas supply means for supplying a predetermined gas into the process chamber, and a shield electrode member placed between the insulating plate and the planar antenna member and including microwave transmission windows respectively corresponding in position to the microwave radiation holes of the planar antenna member for blocking out radiation of the microwave from the center and a part therearound of the planar antenna member.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.